(1) Field of the Invention
This invention relates to a processor controlled communication switching system and, more particularly, to a clock pulse checking circuit for use in such a system.
(2) Description of the Prior Art
In order to provide the necessary reliability required in modern electronic telephone exchanges, duplicate equipment is run in synchronism and other equipment is utilized to monitor it. This is done so that a signal failure will not result in a system outage. The system clock is one of these system modules whose output is essential for the operation of the system. A further requirement is that this output be received at the utilizing modules.
An arrangement for monitoring the system clock operation is disclosed in U.S. Pat No. 3,795,867 issued Mar. 5, 1974 and U.S. Pat. No. 3,803,568 issued Apr. 9, 1974. These patents ensure that clock pulses are available at the output but it cannot monitor the receipt of these pulses of the utilizing module. Further it is not economically feasible to duplicate the transmission paths to these modules.